Plant fibers are as light as about ⅕ the weight of steel and at least about five times stronger than steel, with a linear thermal expansion coefficient as low as 1/50 the linear thermal expansion coefficient of glass.
A technique of producing microfibrillated plant fibers (MFC) by mechanically or chemically defibrating plant fibers is known. MFC is a fiber having a fiber diameter of about 100 nm, a fiber length of about 5 μm or more, and a specific surface area of 250 m2/g. MFC is stronger than undefibrated plant fibers.
However, cellulose contained in plant fibers has three hydroxyl groups per repeating unit in the molecule, and cellulose as the entire plant fiber contains many hydroxyl groups. As a result, cellulose has strong intermolecular cohesion due to hydrogen bonding.
To obtain a plant fiber composite material by compositing plant fibers or MFC with a resin, a technique of fully dispersing plant fibers or MFC in a resin is known. Patent Literature (PTL) 1 discloses a composition comprising a polymeric compound having a primary amino group, a polymeric compound modified with maleic anhydride, microfibrillated plant fibers, and a polyolefin.
PTL 2 discloses a resin composition comprising modified microfibrillated plant fibers esterified with alkyl succinic anhydride and a thermoplastic resin. PTL 3 discloses a dispersion comprising cellulose nanofibers (CNF), a thermoplastic resin, a nonionic surfactant, and a resin composition formed using this dispersion.
In this way, fiber-reinforced composite resin compositions devised to disperse fine cellulose fibers in the resin and reinforced by fine cellulose fibers are disclosed. To obtain an improved fiber-reinforced resin composition, a suitable combination of satisfactorily dispersible fibers and a resin in which the fibers are easily dispersed is necessary.